A few days ago I found a slug in a ball dahlia, the flower no bigger than a child’s fist, the tiny slug curled inside a petal. Just one little decomposer readying themselves for a dewy night and the feast of fall to come, but it brought upon me the perennial autumnal debate I have with myself: Should I tidy the garden now or not?
The argument for leaving plants standing is both aesthetic and ecological: the architecture of plant forms is revealed in winter, birds feed on the seedheads of flowers and beneficial insects such as predatory and parasitoid wasps overwinter in hollow stems.
I learned about the wasps from Claudia Copley, an entomologist at the Royal BC Museum, who made a strong case for leaving the garden wild. I called her after having run two car loads of stemmy clippings to the dump, whilst feeling vaguely guilty and ill-informed.
“To encourage biodiversity and protect pollinating and predatory insects, it’s best to withhold tidying up until spring,” she said.
My actions may peg me as an ageist gardener (or a tired one ready to be done with it all). And it’s true that in my annual beds I follow the ruthless adage: out with the old/in with the new. No dahlia will be running to slime in my garden at the first frost. But Copley’s knowledge has bolstered me to leave my perennial borders standing.
She said that about 30 percent of our native bees live in stems and stalks, the other 70% nest in the ground. The bees need bare soil; mulched or wood-chipped areas don’t work.
If you’ve seen the Mason bee houses consisting of stacked straw, you’ll understand how a garden is rife with holes and hollows for these important pollinators. Copley also pointed out that our native wasps (as opposed to bees) aren’t wasps in the way we might think of them: they’re often much smaller and have specific goals in mind, goals that can help us as gardeners. For example, predatory wasps provision their eggs with paralyzed aphids and moth caterpillars so their young have ready access to food. The parasitoid wasps lay eggs on caterpillars (or as Copley called them ‘defoliators’). Both types of wasps like to overwinter in old beetle pathways in wood, nooks, holes, and tiny openings.
Now I don’t know about you but this summer I’ve seen more aphids than ever before. I’ve had green ones, and olive-coloured ones, and bluish ones and black ones so thick on some stems that any metaphor I could conjure would be too gross to print.
Copley informed me that we have about five hundred species of aphid in BC. After hearing that, I resisted complaining about my garden, but I did query her on ladybugs which have been a blessing to me this year, their striped black and orange larvae visible everywhere on aphid-infected plants.
“They’re introduced,” she told me.
“Really?” I recalled myself a couple of years ago shaking mail-ordered ladybirds from a bag. “Who knew?”
Copley went on to say that native wasps are the bonafide beneficials. Often unseen, but vital to plant health in our region.
Donna Harrison, who tends the perennials at Demitasse in Oak Bay, considers plant health too in the fall. She said she made the mistake of cutting down her grasses last autumn. “The winter was really tough last year. Things froze and thawed and froze again. My grasses came through, but they would have been better off it they’d had a bit of protection.”
Harrison also encourages caution on cutting back plants that have yet to establish themselves. “Having protection over the crown of the plant can help it survive the early years.”
Protecting habitats, protecting plants…this fall won’t be the first time I try to save my garden from myself.